Several different processes have been employed for vapor deposition of thin films. Each has its own advantages and disadvantages. With the advent of superconductivity at relatively high temperatures, e.g. above 30.degree. Kelvin, attention has been focused on certain inadequacies of prior techniques. Many materials, including at least some superconducting materials, include several chemically combined elements. Such a material is here called a complex material, i.e. one which comprises a number of elements of diverse vapor pressures in a specific ratio forming a compound with predetermined properties. Sputtering and co-evaporation have been employed for depositing films of superconducting materials; but both techniques require critical control of both deposition conditions and post-deposition annealing conditions. A Tanaka et al. U.S. Pat. No. 4,604,294 presented the idea of using a pulsed laser beam to evaporate an organic compound and then deposit all of the organic compound vapors in vacuum to form a thin film of the compound on a substrate surface. The film is said to have a chemical structure like that of the compound. U.S. Pat. No. 4,128,121 to Sigsbee and U.S. Pat. No. 4,286,545 to Takagi et al. teach separately evaporating different substances and then mixing the vapors prior to their deposit on a substrate.
Laser induced evaporation has been used for deposition of thin films applied to many materials. "Preparation of Y-Ba-Cu oxide superconductor thin films using pulsed laser evaporation from high T.sub.c bulk material" by D. Dijkkamp et al., Applied Physics Letters, Aug. 24, 1987, Vol. 51, No. 8, pages 619-621, shows the use of pulsed excimer laser evaporation from a bulk target to realize a film resulting from interception of the evaporant plume and having a composition within 10% of the composition of the target material. The target was in the form of a disk shaped pellet that was rotated to obtain a relatively constant deposition rate and to reduce texturing of the irradiated surface of the pellet. The film deposited exhibited a thickness variation in the center of the substrate on which the film was deposited. It has been found, however, that the asserted stoichiometry fidelity was not always reproducible.